(function () {
  var ns = $.namespace('pskl.service');

  var SNAPSHOT_PERIOD = 50;
  var LOAD_STATE_INTERVAL = 50;

  ns.HistoryService = function (piskelController, shortcutService) {
    this.piskelController = piskelController || pskl.app.piskelController;
    this.shortcutService = shortcutService || pskl.app.shortcutService;

    this.stateQueue = [];
    this.currentIndex = -1;

    this.lastLoadState = -1;

    this.saveNextAsSnapshot = false;
  };

  ns.HistoryService.SNAPSHOT = 'SNAPSHOT';
  ns.HistoryService.REPLAY = 'REPLAY';
  /**
   * This event alters the state (frames, layers) of the piskel. The event is triggered before the execution of associated command.
   * Don't store snapshots for such events.
   */
  ns.HistoryService.REPLAY_NO_SNAPSHOT = 'REPLAY_NO_SNAPSHOT';

  ns.HistoryService.prototype.init = function () {
    $.subscribe(Events.PISKEL_SAVE_STATE, this.onSaveStateEvent.bind(this));

    this.shortcutService.addShortcut('ctrl+Z', this.undo.bind(this));
    this.shortcutService.addShortcut('ctrl+Y', this.redo.bind(this));

    this.saveState({
      type : ns.HistoryService.SNAPSHOT
    });
  };

  ns.HistoryService.prototype.onSaveStateEvent = function (evt, stateInfo) {
    this.saveState(stateInfo);
  };

  ns.HistoryService.prototype.saveState = function (stateInfo) {
    this.stateQueue = this.stateQueue.slice(0, this.currentIndex + 1);
    this.currentIndex = this.currentIndex + 1;

    var state = {
      action : stateInfo,
      frameIndex : this.piskelController.currentFrameIndex,
      layerIndex : this.piskelController.currentLayerIndex
    };

    var isSnapshot = stateInfo.type === ns.HistoryService.SNAPSHOT;
    var isNoSnapshot = stateInfo.type === ns.HistoryService.REPLAY_NO_SNAPSHOT;
    var isAtAutoSnapshotInterval = this.currentIndex % SNAPSHOT_PERIOD === 0 || this.saveNextAsSnapshot;
    if (isNoSnapshot && isAtAutoSnapshotInterval) {
      this.saveNextAsSnapshot = true;
    } else if (isSnapshot || isAtAutoSnapshotInterval) {
      state.piskel = this.piskelController.serialize(true);
      this.saveNextAsSnapshot = false;
    }

    this.stateQueue.push(state);
  };

  ns.HistoryService.prototype.undo = function () {
    this.loadState(this.currentIndex - 1);
  };

  ns.HistoryService.prototype.redo = function () {
    this.loadState(this.currentIndex + 1);
  };

  ns.HistoryService.prototype.isLoadStateAllowed_ = function (index) {
    var timeOk = (Date.now() - this.lastLoadState) > LOAD_STATE_INTERVAL;
    var indexInRange = index >= 0 && index < this.stateQueue.length;
    return timeOk && indexInRange;
  };

  ns.HistoryService.prototype.getPreviousSnapshotIndex_ = function (index) {
    while (this.stateQueue[index] && !this.stateQueue[index].piskel) {
      index = index - 1;
    }
    return index;
  };

  ns.HistoryService.prototype.loadState = function (index) {
    try {
      if (this.isLoadStateAllowed_(index)) {
        this.lastLoadState = Date.now();

        var snapshotIndex = this.getPreviousSnapshotIndex_(index);
        if (snapshotIndex < 0) {
          throw 'Could not find previous SNAPSHOT saved in history stateQueue';
        }
        var serializedPiskel = this.getSnapshotFromState_(snapshotIndex);
        var onPiskelLoadedCb = this.onPiskelLoaded_.bind(this, index, snapshotIndex);
        pskl.utils.serialization.Deserializer.deserialize(serializedPiskel, onPiskelLoadedCb);
      }
    } catch (e) {
      window.console.error("[CRITICAL ERROR] : Unable to load a history state.");
      if (typeof e === "string") {
        window.console.error(e);
      } else {
        window.console.error(e.message);
        window.console.error(e.stack);
      }
      this.stateQueue = [];
      this.currentIndex = -1;
    }
  };

  ns.HistoryService.prototype.getSnapshotFromState_ = function (stateIndex) {
    var state = this.stateQueue[stateIndex];
    var piskelSnapshot = state.piskel;

    // If the snapshot is stringified, parse it and backup the result for faster access next time
    // FIXME : Memory consumption might go crazy if we keep unpacking big piskels indefinitely
    // ==> should ensure I remove some of them :)
    if (typeof piskelSnapshot === "string") {
      piskelSnapshot = JSON.parse(piskelSnapshot);
      state.piskel = piskelSnapshot;
    }

    return piskelSnapshot;
  };

  ns.HistoryService.prototype.onPiskelLoaded_ = function (index, snapshotIndex, piskel) {
    var originalSize = this.getPiskelSize_();
    piskel.setDescriptor(this.piskelController.piskel.getDescriptor());
    this.piskelController.setPiskel(piskel);

    for (var i = snapshotIndex + 1 ; i <= index ; i++) {
      var state = this.stateQueue[i];
      this.setupState(state);
      this.replayState(state);
    }

    var lastState = this.stateQueue[index+1];
    if (lastState) {
      this.setupState(lastState);
    }

    this.currentIndex = index;
    $.publish(Events.PISKEL_RESET);
    if (originalSize !== this.getPiskelSize_()) {
      $.publish(Events.FRAME_SIZE_CHANGED);
    }
  };

  ns.HistoryService.prototype.getPiskelSize_ = function () {
    return this.piskelController.getWidth() + 'x' + this.piskelController.getHeight();
  };

  ns.HistoryService.prototype.setupState = function (state) {
    this.piskelController.setCurrentFrameIndex(state.frameIndex);
    this.piskelController.setCurrentLayerIndex(state.layerIndex);
  };

  ns.HistoryService.prototype.replayState = function (state) {
    var action = state.action;
    var type = action.type;
    var layer = this.piskelController.getLayerAt(state.layerIndex);
    var frame = layer.getFrameAt(state.frameIndex);
    action.scope.replay(frame, action.replay);
  };

})();